Cavity termination for microwave oscillators



021mm Uuw c. A. BEATY 3,333,211 CAVITY TERMINATION FOR MICROWAVE OSCILLATORS 5 sheet s 1 Filed Ja 4 66 FIG. 3

FIG. 2

INVENTOR F G. 4 CHARLES A BEATY T ORNEY July 25, 1967 c,A. BEATY 3,333,211

CAVITY wmmmmzoz: OSCILLATORS FOR EIZICRC 5 Sheets-Sheet 2 Filed Jan. 4,

United States Patent 3,333,211 CAVITY TERMINATION FOR MICROWAVE OSCILLATOR?) Iliarles A. Beaty, Tampa, Fla, assignor to Trait Microwave Corporation, Tampa, Fla. Filed Jan. 4, 1966, Ser. No. 518,610 8 Claims. (Cl. 331-98) This application is a continuation-in-part of copending application Ser. No. 271,042, filed Mar. 27, 1963 for Cavity Termination for Microwave Oscillators, now Patent No. 3,249,890 which issued May 3, 1966.

This invention also relates to a cavity termination for microwave oscillators. More specifically it relates to a microwave triode oscillator of the re-entrant type having a low impedance termination which includes a radio frequency choke section operating to prevent the leakage of energy past the termination. The invention is further specifically directed to such an oscillator having incorporated means to improve the amplitude and phase relationship of the feedback energy.

Oscillators of the type here concerned are used in radar and communications applications to provide continuous or pulsed high frequency electrical signals. Usually they employ a coaxial transmission line or cavity having a vacuum tube positioned within the cavity and electrically connected at its plate and cathode to the inner and outer conductors respectively of the line for supply energy thereto. These devices also have a conducting grid member or sleeve electrically connected to the grid of the vacuum tube and extending within the cavity coaxially with the inner and outer conductors thereof. The grid sleeve is the means by which electrical energy from the cavity is coupled hack (fed back) to the tube grid in proper phase and amplitude for oscillatory signal regeneration.

A relatively high direct biasing voltage must be applied between the plate and cathode of the tube, or in other words between the inner and outer conductors of the oscillator, and for this the inner or plate line conductor is extended exteriorly of the cavity and electrically connected to a positive voltage supply. The R.F. energy generated within the cavity is coupled conveniently to the load through a side access opening in the outer conductor.

One difiiculty with microwave oscillators is that the R.F. fields within the oscillator cavity tend to follow the inner conductor or plate line to the outside of the oscillator where they radiate or are otherwise dissipated, thereby disturbing adjacent circuitry and greatly reducing the power available to be coupled to the load. Oscillator efficiency suffers, and in extreme cases the R.F. losses become so great that oscillations can no longer be sustained within the cavity.

Prior microwave oscillators have employed various devices to confine the RF. fields Within the cavity and yet permit high direct voltages to be applied between the inner conductor or plate line and the outer conductor. For example, a bypass capacitor located at the entry of the plate line into the cavity has been utilized for this purpose. More commonly a large diameter quarter-wave choke joint electrically connected to the plate line and slidably mounted Within the cavity itself has been used.

While these prior devices adequately performed their isolating or choking function, they have been found to considerably increase the capacitance between the inn-er and outer conductors. In the case of the bypass capacitor, the large capacity is required to properly isolate the R.F. and direct voltage circuits; while in the case of the choke joint, the large capacitance is due to the large surface area of the joint itself. In any event, this capacitance causes a considerable distortion of the incoming video pulses when the device is operated in the plate pulsed mode.

Moreover, oscillator devices utilizing the choke joints must rely on plate line tuning. There is no room to insert tuning means such as a trimmer capacitor into the cavity. Accordingly, then, tuning range is limited by the small distance through which the choke joint can slide within the cavity.

The operation of re-entrant type microwave oscillators, particularly those of small physical size operating at very high frequencies, further suffers from the fact that it is extremely difficult to achieve an optimum relationship of feedback energy amplitude and phase necessary for optimum performance. Failure to achieve a reasonably close to optimum amplitude and phase relationship of the feedback energy results in a detrimental reduction in the output power developed by the oscillator.

Accordingly, an object of this invention is to provide an improved triode microwave oscillator, capable of CW or pulsed operation, in which the R.F. fields efiiciently confined entirely within the oscillator cavity.

Another object is to provide a re-entrant oscillator of the above character which includes means for improving the relationship of the feedback amplitude and phase.

A further object is to provide a microwave oscillator of the above character which is small, but easy to assemble; inexpensive to manufacture, but rugged, and which suffers substantially no power losses due to unwanted R.F. radiation.

It is a more specific object of this invention to provide an oscillator capable of plate pulsed ope-ration which neither distorts nor otherwise adversely affects the incoming video pulses.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and object of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIGURE 1 is a vertical section of a microwave oscillator embodying our invention, and with portions shown in side elevation;

FIGURE 2 is a view along line 2-2 of FIGURE 1;

FIGURE 3 is a view along line 3-3 of FIGURE 1;

FIGURE 4 is an exploded perspective view of selected portions of the oscillator of FIGURE 1;

FIGURE 5 is an enlarged fragmentary vertical section of the R.F. termination for the microwave oscillator shown in FIGURE 1;

FIGURE 6 is an enlarged view taken along line 6-6 of FIGURE 5;

FIGURE 7 is a vertical section of a modified microwave oscillator constructed according to our invention; and

FIGURE 8 is a vertical section of a further modified microwave oscillator constructed according to our invention.

Referring first to FIGURE 1, the oscillator comprises an elongated, generally cylindrical, tubular outer conductor or shell 10. Shell 10 is formed with a stepped, reduced diameter portion or shoulder 11 set in from the left end thereof for positioning a conventional high frequency triode vacuum tube 12. Tube 12 has the usual heater pins 13, 13, cathode ring 14, grid ring 15 and plate pin 16. When the tube 12 is mounted properly within shell 10, the cathode ring 14 seats in the stepped portion of shoulder 11 thereby locating the tube centrally within the shell and at the same time electrically connecting the cathode ring 14 thereto. A conducting retaining ring 17 is fitted within the end of shell followed by an annular insulating spacer member 18. Filament voltage is applied to the heater pins 13, 13 by means of socket connectors 19, 19 which engage pins 13, 13 and extend on out to the end of shell 10. An insulating disc-like member 21 having suitable pair of openings 22, 22 accommodating the connectors 19, 19 is fitted into the end of shell 10. The entire aforementioned tube assembly is held firmly in place by means of a snap ring 23 which fits tightly in a circumferential groove provided just inside the end of shell 10.

A tubular grid member or sleeve 24, operating in the half wave mode is spaced coaxially within the outer conductor 10. Sleeve 24 extends part way along the length of conductor 10 and its diameter is slightly larger than that of tube 12. The end portion of sleeve 24 facing tube 12 is slotted lengthwise to form an annular array of spring fingers 25 (FIGURES l and 2) which are adapted to engage over and make good electrical contact with grid contact ring 15. The individual fingers 25 are grooved at 27 to maintain secure engagement between sleeve 24 and ring 15. The grid sleeve 24 also is supported by a set of adjustable insulating set screws 28 screwed through threaded openings disposed evenly about the circumference of shell 10 and bearing on the outside of the sleeve. Proper adjustment of screws 28 maintains sleeve 24 in coaxial alignment within conductor 10. A resistor 29 is shown connected between the gridsleeve 24 and cathode ring 14 to provide a DC. return to the grid, although if desired this resistor may actually be built into tube 12.

The oscillator has also an inner conductor or plate line indicated generally at 31 spaced coaxially within shell 10 and also within grid sleeve 24. In the illustrated embodiment the line 31 operates in the threequarter Wave length mode. Plate line 31 comprises an elongated inner line section 32 extending a considerable distance beyond grid member 24. Section 32 has a diameter slightly larger than that of plate pin 16 and is partially slotted lengthwise from the end facing tube 12 so as to form a pair of curved fingers 33 tightly engaging the pin 16. Line section 32 is seen also to be hollowed out at its other end and is internally threaded at 34 to accommodate the correspondingly threaded end 35 of an elongated outer plate line section 36. The other end of line section 36 is flanged at 37 and extends on out to the end of shell 10 where it can be suitably connected electrically at 38 to a constant or pulsed high voltage supply.

In accordance with this invention, means are provided for terminating in a short circuit the coaxial line or cavity formed between the inner and outer conductors 31 and 10 respectively and thereby confining the RF. fields within the oscillator cavity, without short circuiting the high direct voltage between the plate line 31 and outer conductor 10. The terminating means are shown in the illustrated embodiment to comprise a tubular conducting member 39 (FIGURES 1 and 4). Member 39 is secured within so as to make good contact with an enlarged bore portion 41 of shell 10. It is actually made up of two integral portions. The first portion is a thin walled generally cylindrical sleeve portion 42 whose inside diameter is somewhat larger than that of plate line 31 and which is adapted to be positioned coaxially and in closely spaced relation about plate line 31 beyond the free end of grid member 24. The second portion is a circular flange portion 43 arranged in coaxial alignment with the butt end of sleeve 42 facing the open end of shell 10.

An axial opening 44 is formed in disk 43 centrally of sleeve 42 for receiving the plate line 31 in its passage out to the end of shell 10. The diameter of opening 44 is made smaller than that of the bore of sleeve portion a 4 42, thereby forming an annular internal shoulder at 45, the reason being that as mentioned previously, only the outer reduced diameter section 36 of plate line 31 extends to the end of shell 10. The inner line section 32 is seen to terminate at 32a inside the shell 10 within sleeve portion 42.

Thus, when plate line 31 is positioned properly with respect to the conducting member 39, it forms therewith a small diameter, open ended, coaxial transmission line extending from the free end 46 of sleeve 42 to the termination 32a of the inner line section 32. In order for the transmission line to function most efliciently as a choke section, its characteristic impedance should be made as small as possible. Accordingly the spacing between conducting member 39 and plate line 31 should be made small. To insure that these two conductors remain insulated from one another when the customary high plate voltage is applied between plate line 31 and outer shell 10, an insulating sleeve 48 is inserted into the space between sleeve 42 and inner plate line member 32. The sleeve 48 comprises, in the illustrated embodiment, a generally cylindrical tube constructed of a suitable relatively rigid, low-loss dielectric material such as, for example, polytetrafluoroethylene. Sleeve 48 is formed with a major portion 49 fitting snugly within sleeve 42 and around plate line 31; it also has a reduced diameter minor portion 51 fitting snugly within the opening 44 in disk portion 43 of the member 39. The length of minor portion 51 is approximately equal to the thickness of disk portion 43, while the major spacer portion 49 is made longer than and to extend appreciably beyond the left end of sleeve 42 to prevent arcing between sleeve portion 42 and plate line 31.

Still referring to FIGURE 1, spacer portion 49 is provided with an internal bore 52 accommodating the inner plate line conductor 32 and a reduced diameter bore 54 extending through disk portion 43. Bore 54 is internally threaded at 55 to engage a correspondingly threaded shank portion 56 of plate line section 36. A washer 57 constructed of a suitable dielectric material is provided on outer plate line section 36 adjacent to a flange 37 to insulate that from the disk portion 43 of conducting member 39.

As seen in FIGURES 1 and 4, further amplified by FIGURES 5 and 6, the outer plate line section 36 between threaded portions 35 and 56 is of reduced diameter so as to form an air gap between it and the inner plate line section 32. This air gap, indicated at 30 in FIGURES 5 and 6, extends from the termination of the threads 35 to beyond the termination 32a of the inner plate line section 32 where the threads 56 begin. Thus, this air gap 31 constitutes a coaxial transmission line of low characteristic impedance bounded by the inner plate line section 32 and the outer plate line section 36; this transmission line being electrically connected in series at the termination 32a of the plate line section 32 with the coaxial transmission line bounded by the plate line section 32 and the sleeve 42 of termination 39.

These two transmission lines are designed such that their lengths are each substantially equal to a quarterwave length at the operating frequency of the oscillator. Being connected in series at the termination 32a of the inner plate line section 32, their combined length is substantially equal to one-half wave length at the oscillator operating frequency. The termination of the inner transmission line (air gap 30) at the point of threaded engagement between the inner and outer plate line sections (threads 35) is obviously a short circuit. This 10W impedance R.F. termination is reflected as an infinite RF. impedance (maximum R.F. voltage) at the termination 32a of the inner plate line section 32 one-quarter wave length away. This infinite R.F. impedance (open end) is reflected as a low R.F. impedance at the input of the outer transmission line defined by the inner plate line section 32 and the sleeve 42, which is again one-quarter wave length away.

Thus there is provided a double folded R.F. choke terminated in a short circuit thereby reflecting a low R.F. impedance to the input thereof (termination 46 of sleeve 42). With a minimum R.F. voltage condition developed at the input of this double folded choke section, leakage of RF. energy from the oscillator cavity along the plate line section 36 to the exterior is virtually eliminated. This necessary minimum R.F. impedance at the input of the choke is more precisely achieved by reflection from a half wave length choke terminated in a short circuit as herein provided rather than by reflection from a quarter wave length choke terminated in an open circuit. This choking action is eficiently provided without also providing a DC. short circuit between the plate line 31 and the shell 10. Moreover, by virtue of the folded configuration of this choke, the axial length of the oscillator is not increased.

When properly seated within shell 10, the conducting member 39 effectively seals the oscillator cavity against dirt and moisture. Further, the disk portion 43 of member 39 is spaced approximately one-quarter wave length from the free end of grid member 24 so that the plate line 31 can operate as desired in the A wave length mode. Thus energy is coupled back into the grid-cathode line in phase for sustaining oscillations within the cavit Energy may be coupled out of the cavity through a conventional probe, indicated at 58, mounted through the side wall of shell 10.

It is a feature of this invention that the double folded one-half wave length choke section is located substantially at the axis of the oscillator and thus a substantial distance from the shell 10. Accordingly the portion of the oscillator beyond the grid member is free to receive a tuning stub, indicated generally at 59, mounted through the side wall of shell 10. The illustrated tuning stub, which effects capacitance tuning, comprises a threaded screw 61 extending through a correspondingly threaded and partially slitted sleeve 62 integral with shell 10. The outside of sleeve 62 is also threaded and is adapted to receive a correspondingly threaded nut 63 which when screwed down on sleeve 62 squeezes it together and thereby locks the tuning screw 61 in place.

As best seen in FIGURES 1 and 5, the inner end of the tuning screw 51 is free to travel all the way from shell to sleeve 42 or in other words, almost over the entire radius of the oscillator cavity. Accordingly, the oscillator is accurately tunable over a relatively wide range of frequencies as compared with prior comparable devices. Further, the tuning screw 61 can be screwed all the way down so as to touch sleeve 42 without shorting out the high voltage D.C. plate circuit, since both the screw 61 and the sleeve 42 are always maintained at the same direct electrical potential as the outer shell 10.

A further advantage of the centrally located choke section is that a large space is provided within the cavity for accommodating temperature responsive means to com pensate the oscillator for the effects of temperature change. The temperature responsive means shown in the illustrated embodiment (FIGURE 1) comprise three generally L-shaped bimetallic strips 64 disposed radially about the axis of shell 10. The strips 64 are secured at their short legs by rivets 65 to the inside face of disk portion 43. The longer legs of the strips on the other hand are free to swing inwardly toward the sleeve portion 42 when heated, thereby decreasing the capacitance of the anode line and tending to increase the frequency of the oscillator. As seen in FIGURE 1, the ends of strips 64 are free to swing all the Way from outer conductor 10 to sleeve 42. Resultantly they can be made to have extremely sensitive response over a relatively wide range of temperatures. The strips may be arranged to compensate for frequency drift of the oscillator caused by temperature changes and thus stabilize the oscillator frequency. On the other hand, they may be arranged to match the drift of another device, such as a magnetron, used in conjunction with the oscillator.

It should be noted that the centrally-located choke section has substantially no effect on the waveform of the incoming video pulses when the oscillator is operated in the plate pulse mode. This is because the sleeve 42 forming the outer conductor of one choke section is spaced at a considerable distance away from outer conductor (shell 10). Furthermore, its surface area is quite small. The result therefore is that very little capacitance is added to the plate line to effect the arrive time of the incoming pulses at the plate line.

Referring now to FIGURE 7, the modified high frequency oscillator is shown as having an elongated, cylindrical outer conductor or shell 100. A high frequency vacuum tube 102, having an anode pin 104, a grid ring 106, a cathode ring 108, and heater pins 110, is concentrically positioned in the left hand end of the outer conductor 100.

An internal annular shoulder 112 adjacent the left hand end of the shell forms a seat for a tube retaining ring 114. The cathode ring 103 of tube 102 is seated in an annular recess 116 formed in the retaining ring 114. An annular tube retaining nut 118 in threaded engagement with the inner bore of the shell 100 is screwed inwardly against a thrust washer 120 to rigidly clamp the tube 102 in place and to electrically connect the cathode ring 108 to the shell 100.

A termination, generally indicated at 122, physically and electrically terminates the other end of the shell 100. The termination 122 is integrally formed having a radial flange portion 124 and an elongated sleeve portion 126 extending inwardly toward the tube 102. The periphery of the radial flange portion 124 is threaded to engage internal threads 128 formed in the shell 100.

The termination 122 serves to mount a sliding plate line, generally indicated at 130, consisting of an inner section 132, an intermediate section 134, and an outer section 136. The inner section 132 of the sliding plate line 134 is slotted to form a plurality of resilient fingers 132a. The inner ends of the resilient fingers 132a are turned inwardly to engage and make electrical contact with the anode pin 104 of the tube 102.

The intermediate section 134 of the plate line 130 is formed having an enlarged diameter inner portion 134a and a reduced diameter outer portion 134b. The inner portion 134a is f-orce fitted in the central bore 132!) of the inner section 132 of the plate line member 130. The outer portion 134b of the intermediate section 134 is disposed coaxially within the sleeve portion 126 of the termination 122. A dielectric member, generally indicated at 138, and having a radial flange portion 138a and a sleeve portion 138b, is interposed between the termination 122 and the plate line 130 so as to provide isolation between these parts at DC. but to capacitively couple these parts together at RE. The radial flange portion 138:: serves to prevent arcing etween the plate line 130 and the termination 122.

The outer section 136 of the plate line 130 has a threaded inner end engaging a threaded bore 134:: in the intermediate section 134. The mid-portion of the outer section 136 is disposed in coaxially spaced relationship with a counter bore 134d formed in the intermediate section 134. Thus there is provided an elongated annular air gap 140 therebetween which constitutes a quarter wave choke section. This choke section is series connected to a second quarter wave choke section formed between the sleeve portion 134!) of the intermediate section 134 and the sleeve portion 126 of the termination 130. This folded half-wave length choke, which corresponds to the halfwave length choke described in connection with FIG- URES 1 through 6, serves to prevent leakage of RF. energy beyond the termination 122.

Still referring to FIGURE 7, an insulator member, generally indicated at 142, is formed having a hub portion 142a received within the outer end of the sleeve portion 138b of the dielectric 138 and a marginal portion 14 2b accommodated in a recess 124a formed in the outer surface of the radial flange portion 124 of the termination 122. The outer section 136 of the plate line 130 extends through a central bore in the insulator member 142. A washer 144 is fitted on the outer end of the outer section 136 together with an electrical connector 14-6. The connector 146 facilitates electrical connection to a suitable B+ supply. A screw 14-8 threaded into an internal bore in the outer section 136 of the plate line 130 holds the insulator 142, the washer 144 and the connector 146 in place. An annular lock nut 150 engaging the internal threads 128 in the shell 100 is threaded inwardly against a thrust washer 152 to clamp the termination 122 and the plate line 130 in place.

Initial adjustment of the center operating frequency of the oscillator shown in FIGURE 7 may be achieved by manual adjustment of the axial position of the termination 122 and plate line 130. This is accomplished by threading the termination-plate line assembly inwardly until the center operating frequency is achieved. An annular shoulder 154 located at the inner termination of the screw threads 128 prevents the termination 122 from being threaded inwardly to such an extent as to damage the tube 102.

A grid sleeve 156 is slotted to form resilient fingers 156a which engage the grid ring 106 of the tube 102 and thereby concentrically mount the grid sleeve between the shell 100 and the plate 130. As in the oscillator construction of FIGURES 1 through 6, an output connector, generally indicated at 158, extends into the grid-cathode line of the oscillator to extract energy for coupling to a suitable load. Similarly, a tuning screw, generally indicated at 160, adjustably projects into the plate-cathode line of the oscillator to adjust the operating frequency of the oscillator.

According to an additional important feature of the oscillator construction shown in FIGURE 7, the inner section 132 of the plate line 130 is formed with a radially outwardly extending annular knob 162 which is seen to introduce a lumped capacity adjacent the free end of the grid sleeve 156. It has been found that this lumped capacity provided by the annular knob 162 carried on the inner section 132 is effected to materially improve the relationship of the amplitude and phase of feedback relative to the amplitude and phase of the RF. energy developed at the anode of the tube 102. This improvement in the relationship of amplitude and phase of feedback is reflected in an improvement in the available output power for coupling by the output connector 158 to the output load.

Referring now to FIGURE 8, the disclosed high frequency oscillator includes a vacuum tube triode 200 having the typical arrangement of an anode pin 202, a grid ring 204, a cathode ring 206 and heater pins 208. The tube 202 is mounted within one end of an outer shell 210. As seen in FIGURE 8, an annular shoulder 212 is formed in the inner surface of the shell 210 to seat a tube retaining ring 214. An annular washer 216 is seated in a recess 218 formed in the retaining ring 214. The cathode ring 206 of vacuum tube 200 is seated against the washer 216 and a second washer 220 overlies the outer surface of the retaining ring 214 and the cathode ring 206. An annular lock nut 222 engaging an internal threaded portion 224 formed in the left hand end of the shell 210 is threaded inwardly against a thrust washer 226 in mounting the tube 200 within the shell 210. An O-ring 228 interposed between washers 220 and 226 provides some resiliency in the mounting of the tube 200 to protect it againstshock.

Still referring to FIGURE 8, the other end of the shell 210 is terminated by a termination generally indicated at 240. This termination is formed having a radial flange portion 242 and an elongated inwardly extending sleeve portion 244. The outer surface of the flange portion 242 is formed with screw threads to engage an internal threaded portion 246 of the shell 210.

The termination 240 serves to mount a plate line, generally indicated at 250, which consists of an inner section 252, an intermediate section 254 and an outer section 256. The inner section 252 is slotted to form a plurality of resilient fingers 252a with inwardly turned end portions engaging the anode pin 202 of the tube 200. The inner end of the intermediate section 254 is recessed at 254a to receive and hold the outer end of the inner section 252. A reduced diameter portion 25417 of the intermediate section 254 is disposed in coaxially spaced relationship within the sleeve 244 forming part of the termination 240. It will be noted that the outer diameters of the sections 252 and 254 of the plate line 250 and the sleeve 244 of the termination 240 are uniform. This is also true of the oscillator construction of FIGURE 7 except for the knob 160. This construction avoids the introduction of lumped electrical parameters in the oscillator cavities except where desired as in the case of the knob 160.

A dielectric sleeve 258 is interposed between the sleeve portion 254b of the intermediate section 254 and the sleeve 244 of the termination 240. A portion of the dielectric sleeve 258 is extended to overlie a portion of the intermediate section 254 beyond the end of the sleeve 244 so as to prevent arcing between these two parts.

The outer section 256 of the plate line 250 extends concentrically through a counter bore 2540 formed in the intermediate section 254 and threads into a threaded bore 254d. The resulting air gap between the outer section 256 and the intermediate section 254 along the counter bore 254; provides a quarter wave choke section which is series connected with a second quarter wave choke section formed between the intermediate section 254 and the sleeve 244 of the termination 240. As in the other oscillator constructions, this half wave folded choke section prevents leakage of RF. energy from the plate-cathode cavity.

An insulator, generally indicated at 260, is formed having a cup-shaped portion 260a, a central hub portion 26012, and an axial bore 2600. The hub portion 26012 of the insulator 260 is fitted within the left-hand end of the dielectric sleeve 258. The outer section 256 of the plate line 250 extends through the central 'bore 2600 and is fitted with a terminal 262 disposed within the cup portion 260a of the insulator 260. Terminal 262 facilitates conneetion to a power supply providing B+ voltage via the plate line 250 to the anode pin 202 of the tube 200. The insulator 260 serves to insulate the plate line 250 from the termination 240 and also to insure coaxial mounting of the plate line. An annular lock nut 264 threaded on the internal thread 246 of the shell 210 serves to clamp the termination-plate line assembly in place.

Initial adjustment of the operating frequency of the oscillator of FIGURE 8 may be accomplished by rotation of the termination 240 to establish the operating frequency of the oscillator. The annular lock nut 264 then is used to clamp the termination-plate line assembly at the established axial position. A shoulder 265 at the inner termination of threads 246 prevents damage to the tube 200 during this initial adjustment.

A grid sleeve 266 disposed coaxially between the shell 210 and the plate line 250 is slotted to form a plurality of resilient fingers 266a which engage the grid ring 204 of the tube 200. A resistor 268 electrically connected between the cathode ring 206 and the grid ring 204 provides a DC. return path to the grid of the tube 200. A tuning screw, generally indicated at 270, adjustably projects into the plate-cathode cavity of the oscillator to provide for further adjustment of the operating frequency of the oscillator.

In addition to the feature of the folded half-wave choke for preventing leakage of RF. energy beyond the termination 240, an additional important feature of the oscillator construction of FIGURE 8 is the inclusion of an annular dielectric slug 272 in the grid-cathode line adjacent the free end of the grid sleeve 266. It has been found that in addition to the mechanical function of concentrically mounting the grid sleeve 266, the annular dielectric slug 272 additionally serves an important electrical function. Specifically, this dielectric slug 272, which introduces a lumped electrical parameter, is found to materially improve the relationship of amplitude and phase of feedback relative to the amplitude and phase of the RF. energy developed at the plate of the tube 200. This improvement in amplitude and phase feedback is reflected in an increase in available power for coupling by an output connector (not shown) to an output load.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efiiciently attained and, since certain changes may be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention, which, as a matter of language, might be said to fall therebetween.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A microwave oscillator, comprising, in combination:

(A) a tubular outer conductor;

(B) a vacuum tube mounted coaxially within one end of said outer conductor, said tube having (1) a cathode electrode electrically connected to said outer conductor,

(2) an anode electrode, and

(3) a grid electrode;

(C) an elongated plate line conductor disposed coaxially within said outer conductor and electrically connected at one end to said anode electrode, said plate line conductor including (1) means forming a first coaxial transmission line,

(a) one end of said first coaxial transmission line nearest said tube being short-circuited, and

(b) the other end being open-circuited;

(D) a grid sleeve disposed coaxially between said outer conductor and said plate line conductor, said grid member (1) being electrically connected to said grid electrode, and

(2) having a free end beyond which said outer and plate line conductors cooperate to define a plate-cathode cavity; and

(E) means terminating said plate-cathode cavity, said terminating means including (1) an electrically conducting sleeve disposed coaxially about and in closely spaced relationship to said plate line conductor so as to define a second transmission line coextensive wit-h said first transmission line,

(a) said second transmission line being electrically connected in series with said first transmission line at the open-circuited end of said first transmission line to provide -a double folded choke for preventing leakage of R.F. energy from said plate-cathode cavity, and

10 "(2) a radial flange fixedly mounted within the other end of said outer conductor, said radial flange (a) electrically connecting said conducting sleeve to said outer conductor so as to electrically terminate said plate-cathode cavity, and (b) having a central hole through which the other end of said plate line conductor projects for connection to an external power supply.

2. The device defined in claim 1 wherein said plate line conductor is formed of at least two parts,

(1) one of said parts being a first elongated member having (a) an inner end electrically connected to said anode terminal,

(b) an outer end, and

(c) an axial bore extending inwardly from said outer end, and

(2) the other of said parts being a second elongated member extending into said axial bore and having (a) an inner end physically engaging and electrically contacting said first member,

(b) an outer end extending beyond said outer end of said first member for connection to the external power supply, and

(c) an intermediate portion extending from a point adjacent said inner end of said second member to a point substantially beyond the outer end of said first member,

(i) said intermediate portion in said bore being radially spaced from said first member to define said first transmission line short-circuited at the inner end of said second member and open-circuited at the outer end of said first member.

3. The device defined in claim 1 wherein the combined length of said first and second transmission lines is approximately equal to one-half wavelength at the center operating frequency of said oscillator.

4. The device defined in claim 1 which further includes (F) an insulating sleeve disposed between said conducting sleeve and said plate line conductor,

(1) whereby said plate line conductor and said outer conductor are insulated from each other at DC. but capacitively coupled together at RR 5. The device defined in claim 2 wherein the inner end of said second member is provided with screw threads for engaging internal screw threads in said first member.

6. The device defined in claim 5 which further includes (F) an element disposed about the central hole in said flange to insulate the outer end of said second member from said flange.

7. A microwave oscillator, comprising, in combination:

(A) a tubular outer conductor;

(B) a vacuum tube mounted coaxially within one end of said outer conductor, said tube having (1) a cathode electrode electircally connected to said outer conductor,

(2) an anode electrode, and

(3) a grid electrode;

(C) an elongated plate line conductor disposed coaxially within said outer conductor and electrically connected at one end to said anode electrode, said plate line conductor including (1) means forming a first coaxial transmission line,

(a) one end of said first coaxial transmission line nearest said tube being short-circuited, and

(b) the other end being open-circuited;

(D) a grid sleeve disposed coaxially between said outer conductor and said plate line conductor, said grid member (1) being electrically connected to said grid electrode, and

(2) having a free end beyond which said outer and plate line conductors cooperate to define a plate-cathode cavity; and

(E) means terminating said plate-cathode cavity, said terminating means including (1) an electrically conducting sleeve disposed coaxially about and in closely spaced relationship to said plate line conductor so as to define a second transmission line coextensive with said first transmission line,

(a) said second transmission line being electrically connected in series with said first transmission line at the open-circuited end of said first transmission line to provide a double folded choke for preventing leakage of radio frequency energy from said platecathode cavity, and

(2) a radial flange fixedly mounted within the other end of said outer conductor, said radial flange (a) physically contacting said outer conductor and electrically connecting said outer conductor to said conducting sleeve so as to electrically terminate said plate-cathode cavity,

(b) the point of physical contact between said flange and said outer conductor nearest said tube being radially aligned with the inner surface of said flange, and

(c) having a central hole through which the other end of said plate line conductor projects for connection to an external power supply.

8. A microwave oscillator, comprising, in combination:

(A) a tubular outer conductor;

(B) a vacuum tube mounted coaxially within one end of said outer conductor, said tubing having (1) a cathode electrode electrically connected to said outer conductor,

(2) an anode electrode, and

(3) a grid electrode;

(C) an elongated plate line conductor disposed coaxially Within said outer conductor and electrically connected at one end to said anode electrode, said plate line conductor including ,(1) means forming a first coaxial transmission line,

(a) one end of said first coaxial transmission line nearest said tube being short-circuited, and

(b) the other end being open-circuited;

(D) a grid sleeve member disposed coaxially between said outer conductor and said plate line conductor, said grid sleeve member (1) being electrically connected to said grid electrode, and

(2) having a free end beyond which said outer and plate line conductors cooperate to define a platecathode cavity; and

(E) means terminating said plate-cathode cavity, said terminating means including (1) an electrically conducting sleeve disposed c0- axially about and in closely spaced relationship to said plate line conductor so as to define a second transmission line coextensive with said first transmission line,

(a) said second transmission line being electrically connected in series with said first transmission line at the open-circuited end of said first transmission line to provide a double folded choke for preventing leakage of radio frequency energy from said platecathode cavity, and

(2) a radial flange fixedly mounted within the other end of said outer conductor, said radial flange (a) electrically connected said conducting sleeve to said outer conductor so as to electrically terminate said plate-cathode cavity, and

(b) having a central hole through which the other end of said plate line conductor projects for connection to an external power pp y (F) an insulating sleeve disposed between said conducting sleeve and said plate line conductor,

(1) whereby said plate line conductor and said outer conductor are insulated from each other at direct current but capacitively coupled together at radio frequencies (2) the inner end of said insulating sleeve extends beyond the inner end of said conducting sleeve to prevent arcing between said conducting sleeve and said plate line conductor, and

(3) the outer end of said insulating sleeve extends substantially through the central hole in said flange.

References (Iited UNITED STATES PATENTS 2,874,288 2/1959 Jatfe 331-98 ROY LAKE, Primary Examiner.

J. B. MULLINS, Examiner. 

1. A MICROWAVE OSCILLATOR, COMPRISING, IN COMBINATION: (A) A TUBULAR OUTER CONDUCTOR; (B) A VACUUM TUBE MOUNTED COAXIALLY WITHIN ONE END OF SAID OUTER CONDUCTOR, SAID TUBE HAVING (1) A CATHODE ELECTRODE ELECTRICALLY CONNECTED TO SAID OUTER CONDUCTOR, (2) AN ANODE ELECTRODE, AND (3) A GRID ELECTRODE; (C) AN ELONGATED PLATE LINE CONDUCTOR DISPOSED COAXIALLY WITHIN SAID OUTER CONDUCTOR AND ELECTRICALLY CONNECTED AT ONE END TO SAID ANODE ELECTRODE, SAID PLATE LINE CONDUCTOR INCLUDING (1) MEANS FORMING A FIRST COAXIAL TRANSMISSION LINE, (A) ONE END OF SAID FIRST COAXIAL TRANSMISSION LINE NEAREST SAID TUBE BEING SHORT-CIRCUITED, AND (B) THE OTHER END BEING OPEN-CIRCUITED; (D) A GRID SLEEVE DISPOSED COAXIALLY BETWEEN SAID OUTER CONDUCTOR AND SAID PLATE LINE CONDUCTOR, SAID GRID MEMBER (1) BEING ELECTRICALLY CONNECTED TO SAID GRID ELECTRODE, AND (2) HAVING A FREE END BEYOND WHICH SAID OUTER AND PLATE LINE CONDUCTORS COOPERATE TO DEFINE A PLATE-CATHODE CAVITY; AND (E) MEANS TERMINATING SAID PLATE-CATHODE CAVITY; SAID TERMINATING MEANS INCLUDING (1) AN ELECTRICALLY CONDUCTING SLEEVE DISPOSED COAXIALLY ABOUT AND IN CLOSELY SPACED RELATIONSHIP TO SAID PLATE LINE CONDUCTOR SO AS TO DEFINE A SECOND TRANSMISSION LINE COEXTENSIVE WITH SAID FIRST TRANSMISSION LINE, (A) SAID SECOND TRANSMISSION LINE BEING ELECTRICALLY CONNECTED IN SERIES WITH SAID FIRST TRANSMISSION LINE AT THE OPEN-CIRCUITED END OF SAID FIRST TRANSMISSION LINE TO PROVIDE A DOUBLE FOLDED CHOKE FOR PREVENTING LEAKAGE OF R.F. ENERGY FROM SAID PLATE-CATHODE CAVITY, AND (2) A RADIAL FLANGE FIXEDLY MOUNTED WITHIN THE OTHER END OF SAID OUTER CONDUCTOR, SAID RADIAL FLANGE (A) ELECTRICALLY CONNECTING SAID CONDUCTING SLEEVE TO SAID OUTER CONDUCTOR SO AS TO ELECTRICALLY TERMINATE SAID PLATE-CATHODE CAVITY, AND (B) HAVING A CENTRAL HOLE THROUGH WHICH THE OTHER END OF SAID PLATE LINE CONDUCTOR PROJECTS FOR CONNECTION TO AN EXTERNAL POWER SUPPLY. 